Mobile or wireless communications networks are capable of carrying circuit-switched and packet-data traffic (e.g., voice traffic, data traffic, etc.) between a mobile device and some other endpoint or endpoints. The endpoint can be another mobile device or a device connected to a network such as a public switched telephone network (PSTN) or a packet data network. Traditional wireless protocols provide for circuit-switched communications between devices, such as the circuit-switched protocol provided by 1xRTT, as defined by CDMA (code division multiple access) 2000. With circuit-switched communications, a dedicated circuit or channel is established between nodes and terminals to allow communication between endpoints. Each circuit or channel that is dedicated cannot be used by other users until the circuit or channel is released.
In contrast, with packet-data communications, data is split into packets, with the packets routed individually over one or more paths. A widely-used protocol for transporting packet-data communication information is Internet Protocol (IP). Examples of packet-data communications that are possible over packet-data networks include electronic mail, web browsing, file downloads, electronic commerce transactions, voice or other forms of real-time, interactive communications, and others.
To provide wireless access to a packet-data network, a wireless access network according to any of the following standards can be used: EV-DO or EV-DV (also referred to as HRPD or high rate packet data), as defined by the CDMA 2000 family of standards; WiFi; WiMax (Worldwide Interoperability for Microwave Access); and others.
It is common for circuit wireless access networks (such as those based on 1xRTT) to coexist with packet-data access networks within a communications network. Certain mobile devices are able to operate with both circuit wireless access networks and packet-data wireless access networks. Such mobile devices are referred to as multi-mode mobile devices.
Conventionally, when a multi-mode mobile device transitions from a packet-data wireless access network, such as an EvDO access network, to a circuit wireless access network, such as a 1xRTT access network, a relatively large voice gap can occur during the handoff. A “voice gap due to handoff” refers to a time duration during which voice bearer data is not being exchanged between the mobile device and some other endpoint as a result of the mobile device transitioning from one access network to a different access network. A long voice gap can be bothersome to the users involved in the call session, and sometimes may even result in the call being dropped by one of the users.